An OFDMA-TDMA system uses OFDM (Orthogonal Frequency Division Multiplex) for modulation and demodulation of data and uses TDMA (Time Division Multiple Access) for user multiplexing. The OFDMA-TDMA system has a coordinator that manages and schedules bandwidths such that, when a terminal requiring to transmit data requests the OFDMA-TDMA system to allocate a bandwidth, the coordinator allocates the bandwidth to the terminal. Then, the terminal transmits data using the allocated bandwidth.
FIG. 1 illustrates layers of a wireless Internet system. Referring to FIG. 1, the wireless Internet system includes a physical layer 100, a MAC layer 200, and a network layer 300. These layers can be called first, second and third layers L1, L2 and L3, respectively. If required, the wireless Internet system can further have upper layers.
The physical layer 100 manages a modulation method and multiple access RF processing and the MAC layer 200 takes charge of a function of controlling access of the physical layer, such as address allocation, access coordination and frame checking. The network layer 300 manages routing and congestion control. The layers 100, 200 and 300 control an operation between adjacent layers through server access points 10 and 20.
FIG. 2 illustrates a frame structure of a conventional OFDMA-TDMA system. Referring to FIG. 2, a MAP 101, which is a MAC layer message, defines the number of resources and sub channels allocated by a terminal and serves as indexes of designating components of a downlink burst DL-BURST 102 and an uplink burst UL-BURST 103 that follow the MAP 101. The MAP 101 is classified into an uplink MAP UL-MAP and a downlink MAP DL-MAP depending on a link direction.
If a terminal previously requests an OFDMA-TDMA system to allocate a specific bandwidth, the coordinator of the OFDMA-TDMA system allocates the bandwidth to the frame. Then, the terminal analyzes the MAP 101 to confirm whether there is a bandwidth allocated thereto and transmits data using a bandwidth allocation interval 104 indicated by the MAP 101.
MAC is a protocol located above the physical layer managing RF and modem. Thus, data of the MAP 101 should be subjected to processes required for receiving RF and modem signals in order to reach the MAC layer. This generates a predetermined delay time 105.
Furthermore, when the MAC requires to transmit data in synchronization with a designated interval, the data must be subjected to processes required for transmitting RF and modem signals. Thus, the data should be transmitted a predetermined delay time 107 ahead of the actual data transmission time. Accordingly, the MAC of the terminal should begin to prepare data to be transmitted the RF/modem reception delay time 105 behind the moment of time when the frame of the data actually starts and end the preparation of the data the RF/modem transmission delay time 107 ahead of the time interval during which the bandwidth required for transmitting the data is allocated to the terminal.
When the ratio of the downlink burst DL-BURST to the uplink burst UP-BURST is approximately 7:3 and the modem/RF reception delay time 105 and transmission delay time 107 respectively occupy ⅓ of the downlink burst DL-BURST 102, a period of time required for the terminal to prepare a PDU (Protocol Data Unit) corresponds to approximately ⅓ of the downlink burst DL-BURST 102. The ratio of each of the modem/RF reception delay time 105 and transmission delay time 107 to the entire frame interval is 7/10×⅓, which corresponds to approximately ¼ of a single frame interval. This is very short time such that each of the modem/RF reception delay time 105 and transmission delay time 107 becomes 1.35 msec when a single frame interval is 5 msec.
The terminal should transmit data based on QoS. QoS means network capability providing a method of reducing network traffic or making a reservation of some of bandwidths in advance. Network managers provide QoS to their networks in many ways. QoS does not mean 100% guarantee of bandwidths or packet loss rate of 0%. However, the network managers manage traffic transmission using a method of transmitting a specific traffic more rapidly or making a reservation of network bandwidths through QoS.
A variety of techniques with respect to QoS, such as IEEE 802.1p, differential service, RSVP (Resource Reservation Protocol), IP multiplexing and so on, have been disclosed.
For QoS, it is required that data packets to be transmitted are classified, priorities of the data packets are determined in consideration of importance or urgency of the data packets, and the data packets are transmitted based on their priorities. Here, an internal algorithm is executed with reference to a profile including QoS characteristic. This process is an operation with high complexity and thus the operation is generally processed by software.
However, a period of time during which a terminal recognizes bandwidth allocation and then transmits data using the allocated bandwidth is very short. Thus, QoS-based data transmission is difficult to carry out by software within the period of time. If the QoS-based transmission is executed by hardware, it is difficult to finely control the QoS-based transmission in various manners though the transmission can be carried out within the period of time.
Furthermore, when the coordinator allocates a bandwidth to the next frame not the current frame, the terminal is given extended time including a single frame interval added thereto and thus the QoS-based data transmission can be performed by software. In this case, however, data transmission is delayed due to the extended time given to the terminal. This can deteriorate quality of upper application programs and bring about serious problems in the case of real-time application.
As described above, when the terminal transmits uplink data based on QoS in the OFDMA-TDMA system, there are problems in both cases of processing the data transmission by software and hardware.